1. Field of the Invention
The present invention relates to a tape cartridge, and more particularly to an enforcing rib provided to a hub pawl of a tape winding hub.
2. Description of the Related Art
As shown in FIG. 1, a tape cartridge in a prior art is constructed so that plastic (generally, high-impact polystyrene) hubs 12 around which a tape 11 is wound are freely rotatably located on respective driving shaft insertion holes 13 at the right and left sides in a main body case 10. Each of both the ends of the tape 11 is hooked and coupled to a part of each outer periphery of the right and left hubs 12 by a cramping piece 14, and the tape 11 is drawn from one hub 12 to the front face of the main body case 10 and wound by the other hub 12.
The hub 12 has a hub hole 15 at the center thereof, and a plurality of hub pawls 16 are integrally projected from the inner peripheral surface of the hub hole 15 in the central direction so as to be spaced from one another at predetermined intervals.
The hub pawl 16 is designed in a substantially cylindrical shape of about 1.5 mm in diameter and about 1 mm in length, and it is extremely smaller as compared with the size, thickness, etc. of the overall hub 12. Therefore, fast feeding or rewinding operation by a recent tape recorder imposes a large impact load on the hub pawls 16, and excessive stress is applied to the bases of the hub pawl 16, so that such a problem as damage or the like may occur. Particularly since there frequently occurs such a case that a user carries a tape cartridge on the road when the user goes outdoors, when a drop impact or the like is applied to a tape cartridge while the tape cartridge is accommodated in an accommodation case, a hub rotation stop member at the accommodation case side and the hub pawls 16 collide against each other, and the hub pawls 16 may be damaged at the base portions thereof.
JP-A-60-51685U previously proposed a device of a countermeasure of preventing the damage of the hub pawls 16 as described above. In this device, as shown in FIG. 2, the base portion of the hub pawl 16 in the rotational direction is provided with ribs 18 each comprising a rounded R-surface 17. By forming the R-surface 17 as described above, the concentration of the excessive stress due to the impact load which is applied to the hub pawls 16 in the rotational direction can be avoided, and the strength can be enhanced, so that the damage preventing effect of the hub pawls 16 can be expected.
However, in case of the hub pawl 16 having the ribs 18 having the R-surface 17 as described above, when the hub 12 is manufactured, it is necessary to process the place of a die corresponding to the R-surface portion of the hub pawl in a minute and complicated three-dimensional shape, and it is difficult or impossible to perform the processing by using equipment such as an electric discharge machine or the like. Therefore, there is a problem that the cutting work must be manually carried out on the place.
In order to solve this problem, there is known JP-A-62-80280U. In this device, as shown in FIGS. 3 and 4, the rib 19 provided to the base of the hub pawl 16 is designed in a simple two-dimensional shape to have an R-surface 20. That is, as shown in FIG. 4, the rib 19 has the R-surface 20 provided in the rotational direction of the hub 12, and side surfaces 22 which are crossed to the R-surface 20 through the ridgelines at both the sides of the R-surface 20, and the R-surface 20 is designed to have the same curvature in the pawl peripheral direction W. The rib 19 of the hub pawl 16 is designed in such a two-dimensional simple shape as described above, so that the electric discharge machining to form a die can be performed and the die processing can be facilitated.
However, even when the R-surface of the rib provided to the hub pawl in the prior art described above is designed in a simple two-dimensional shape, the shape of an electrode required for the electric discharge machining to form a die must be processed in conformity with the shape of the rib. Therefore, there is a problem that the shape of the electrode is complicated.
Accordingly, there is a problem that a rib must be designed in such a shape that an electrode for the electric discharge machining used to process a die for the rib provided to the hub pawl is simple.